RAMMASUN MAKES WAY FOR MATMO AS TROPICAL STORM WALI GOES ‘POOF' & ATLANTIC 'STIRS'

(By Steve Gregory - Substituting for Dr. Masters who is on Vacation.)




Just before 00Z today, Typhoon Rammasun made it’s final landfall in northern-most Vietnam as a CAT 2 (my analysis) and is QUICKLY weakening and losing its identity as it continues moving inland.

Meanwhile, Tropical Storm MATMO (10W) continues to become better organized, and is currently approaching Typhoon intensity. The cyclone has an estimated pressure of 975 mb, and was last located near 11.9N / 130W, or about 600 NM East-Southeast of Manila, Philippines, moving WNW at about 5Kts



Fig 1: Color enhanced IR image of Tropical Storm MATMO. The storm has had several convective bursts over the last 24 hours, and has gradually intensified to near Typhoon intensity, based on Dvorak estimates of T3.5 earlier today. However, ‘Experimental’ satellite derived wind estimates show a considerably weaker system, with MAX winds around 50Kts.

Microwave imagery shows a somewhat elongated structure to the convective banding in the southern semi-circle, but satellite imagery loops show a definite improvement in the over all symmetry of the storm, and there is good consensus between the various agencies that MATMO has sustained winds of 60 Kts.



Fig 2: The upper air wind analysis shows good equatorward outflow, and improved outflow to the west. However, at this time, outflow from the NW – N – E is poor.



Fig 3: Wind shear over the storm center is a moderate 20Kts, which is slowing the rate of intensification.

As the storm moves northwestward, the cyclone will find a region of lowering wind shear, with all dynamic models now in agreement that the high level anti-cyclone now centered about 100 NM to the north of the storm, should become vertically aligned with the lower level circulation center (LLCC). This general fall-off of wind shear along with the overall improvement in the outflow pattern, should support a more rapid intensification phase beginning in about 24-36 hours. In addition to a more conducive atmospheric environment, SST’s and total Ocean Heat Content (OHC) in the vicinity of the storm – including the projected track - will also support a faster intensification rate for the next 72 hours.



Fig 4: The last available HWRF track guidance continues to be in excellent agreement with the last several GFS and EURO model predictions taking the storm across Taiwan around 03Z-06Z Wednesday. It should be noted that the official Forecast from the Japan Meteorological Agency (not shown) calls for the storm to pass well south of Taiwan on Wednesday.

As shown in the below figure, there is nearly unanimous agreement of all specialized hurricane forecast intensity models that MATMO will reach CAT 2 intensity in 36-48 hours, with the HWRF calling for a solid CAT 3 intensity in 72 -84 hours. This forecast seems quite likely to verify.



Fig 5: Last available run of the intensity model forecast suite show MATMO reaching CAT 3 intensity Monday, and this is closely supported by the most recent 12Z GFS global model run that has just come in.

All of the specialized hurricane forecast models are in generally good agreement that MATMO will intensify to CAT 2 by the time it approaches Taiwan by the middle of next week. A couple models are calling for a much stronger storm – though these appear to be outliers at this point (as are some of the Japanese models that originally showed a more northerly track towards Japan). It is worth noting that after 6 model runs forecasting only minor development, the GFS has come back into excellent agreement with the Hurricane models in forecasting a vigorous cyclone, tracking it towards Taiwan.



Fig 6: The official forecast track from JTWC calls for MATMO to make landfall along the central east coast of Taiwan around 06Z Wednesday as a very strong CAT 2. *** Based on the most recent GFS model run – this still appears ‘on track’ ***.

It should be noted that the latest 12Z GFS forecast calls for the storm to take a more westward track after making landfall on Taiwan, eventually making a second landfall on the east coast of China about 24 hrs later. This ‘westward’ turn is likely a contributing factor for the JMA track forecast that now calls for MATMO to pass SOUTH of Taiwan on WED.

WALI ‘VANISHES’




By 00Z last night, ‘WALI’ essentially fell apart. (This assumes it actually ‘existed’ as a Tropical Storm to begin with.)

ATLANTIC REMAINS UNEVENTFUL BUT IS BECOMING MORE ‘INTERESTING’



Fig 7: There are 4 significant waves traversing the tropics – with the CARIB wave (that brought some significant convection to the SE CARIB yesterday) weakening significantly over the last 12 hours. The next wave in the central ATL will reach the SE CARIB by Monday.

The most significant waves of interest today is the fairly significant wave to the West/Southwest of the Cape Verdes along 30W that brought a moisture surge along with it, and the wave just now coming off the West African coast. This second wave along the African coast has an elongated Vorticity pattern associated with it, though no rotation of any type can be discerned in SAT imagery. The lead wave near 30W which brought a large moisture surge (see below 2 figures) with it, is currently moving westward at 12 Kts, while the second wave is westbound at 15Kts. Warm air associated with the Saharan Air Layer has effectively capped convection within the moisture ‘surge’ and is also stifling convection with the wave right along the coast.



Fig 8: The derived precipitable water image shows the large moisture surge associated with the wave near 30W, and in general, the increasing aerial extent of moisture laden air associated with all of the easterly waves.



Fig 9: The overall increase in moisture throughout the tropics – and the general decrease in dry air intrusion into the tropics, is evident in this AM’s water vapor image of the ATL basin.



Fig 10: The last image shows the large scale decrease in adverse wind shear from the CARIB to the African coast.

What makes these waves especially ‘interesting’ is the GFS models' handling of them – with the latest run attempting to spin up a small circulation center by Monday in the vicinity of 40W. While the development of a cyclone seems very unlikely considering the overall stability of the atmosphere and lack of rotation, it does represent a general evolution towards a more conducive environment for the formation of cyclone during the next 7-14 days.

Indeed, the last few GFS model runs have shown a trend towards stronger easterly waves, and ones that are coming off the African coast at somewhat higher latitudes. Combined with a slow but steady decrease in observed wind shear across the ATL tropical basin – and a general moistening of the atmosphere – stability should decrease over the coming 10-15 days, which will provide a more favorable environment for cyclone development.


I will have a brief update tomorrow evening, with a complete update Monday afternoon.

Steve Gregory